Hydrogenation is one of the most widely used and extensively studied methods in synthetic organic chemistry. The ionic hydrogenation reaction is based on the principle that the carbonium ion, formed by protonation of a double bond, reacts with an hydride ion donor (proton and electron pair) to form the hydrogenation product as follows: ##STR2## In this ionic hydrogenation reaction, the hydrogenating pair consists of a proton donor and an hydride ion donor. The hydrogenating pair must meet the following requirements. First, its components must not react with each other. Second, they should not be involved in side reactions with the substrate. Third, the hydrogenation agents and their conversion products must not hinder the evolution of the reduced compounds. In these respects, the pairs involving strong acids and organosilanes have proved most useful. As is usually the case with electrophilic addition, ionic hydrogenation is essentially accompanied by trans-addition of the proton and the hydride ion to the double bond. For example, hydrogenation of 2,3-dimethylindole results essentially in trans-2,3-dimethyl-2,3-dihydroindole, trans:cis ratio being 1.4:1 at 60.degree. C. See Kursanov et al., Synthesis 9, 633 (1974).